I too first thought it might have something to do with the tint or color, but wouldn't this mean that he would also get the same problems when looking at neon or fluorescent light? Or some monitors even? Those can all get pretty cool/blue and there's not a single problem with those....
I still think this is another one of those miss-diagnosed 'allergies', kind of like the one my misses used to have. When she was a kid she once ate something with cheese and got mighty sick after, conclusion she is allergic to cheese (actually diagnosed by her mom and sort of confirmed by a doctor)! Nobody even though about the possibilities of something else apparently. So they never gave her cheese ever again and she grew up thinking she actually was allergic! Now i have quite some allergies myself and i think its really important to know how your body reacts with this sort of thing so i told her to just start eating cheese and guess what? Nothing! Not even an itch, and even worse; she likes cheese!!!
Its a real shame i don't know this person myself, i would have a field-day shining all my flash-lights in his face all day long to see what happens. I bet that its not the led light but that it in fact
is the PWM because i've heard problems like that before and that this diagnosis has been determined simply because doctor nor patient knows anything about the technology behind leds.......
That, or there maybe
is something harmfull in LED lighting, in that case us flashaholics could all get very very sick very very soon.